The present invention relates to an air filter for an internal combustion engine including an air filter housing, walls of which encompass a filter chamber, a filter element positioned in the filter chamber, an air filter housing intake, and an air filter housing exhaust. The invention also concerns a process of modulating noise during operation of an internal combustion engine.
One air filter for an internal combustion engine is known from German publication DE 199 40 610 A1, in which it is proposed that one wall of the air filter housing be provided with a diaphragm made of a material that is less resistant to sound waves than the housing wall itself. This is intended to produce a directed generation of sound, allowing the driver to receive adequate information regarding the engine""s operating conditions. With this embodiment, however, there is no transmission of airborne noise through the filter housing; consequently, an effective modulation of the induction noise can be achieved only within certain limits.
It is thus one object of the invention to develop a device through which modulation of induction noise can be improved.
This object is attained by providing openings in at least one of the walls of the air filter housing, and by sealing off or opening up the openings depending upon operating conditions of the internal combustion engine.
In operation of the internal combustion engine, airborne noise is transmitted through the air filter housing into the engine compartment through the openings in a wall of the air filter housing. As a result, depending upon the operating conditions of the internal combustion engine, the acoustic pattern within the passenger compartment of the vehicle can be improved as necessary. Under certain operating conditions, however, e.g., in cases of low load and speed, to prevent an intake of warm air that would reduce the output of the internal combustion engine, these openings are designed so that they can be closed. At high loads and speeds, these airborne noise passageways can then be opened, in order to ensure an attractive sound inside the compartment. Furthermore, with the additional openings in the air filter, pulsations in the intake air are reduced, and the air filter housing is less prone to vibration.
With features specified in dependent claims, additional advantageous embodiments of the invention are possible.
In a first embodiment, the closeable openings in the air filter housing are converted in a simple manner using a plate element that is provided with openings and is positioned inside the air filter housing; this plate element operates in conjunction with the openings in one wall of the air filter housing as a sort of sliding register.
The plate element that is provided with the openings can be controlled in a simple manner via an actuator, which is connected to a vacuum tank.
The plate element lies advantageously on the base panel of the air filter housing, as an underbody, and is guided along two rails oriented along the two lengthwise sides of the plate element, which are fastened to the wall of the housing that is equipped with the openings.
In a second embodiment, the openings in one wall of the air filter housing are monitored using flexible flap elements. In this case, the control of the flaps is accomplished via the pressure ratios that prevail within the air filter. At low load and speed, the flaps are closed; at high load and speed and corresponding air flow mass, the vacuum conditions prevailing within the air filter housing increase, and the flexible flaps clear the openings in the air filter housing.
The invention is specified in greater detail in the following description and drawings.